1. Field of the Invention
The present invention relates to a method for producing an optical semiconductor device.
2. Description of the Related Art
Non-Patent Document 1 (K. Tsuzuki, T. Ishibashi, T. Ito, S. Oku, Y. Shibata, R. Iga, Kondo and Y. Tohmori, 40 Gbit/s n/i/n InP Mach-Zehnder modulator with a π voltage of 2.2 V, Electronics Letters Online 2nd, October 2003, Vol. 39 No. 20) describes a Mach-Zehnder modulator. The Mach-Zehnder modulator includes a high-mesa-shaped semiconductor layer disposed on a semiconductor substrate. The high-mesa-shaped semiconductor layer is buried with a protective layer. Thus, the semiconductor layer has a side surface on which the protective layer is disposed.